Physical interactions between proteins are critical in executing various cellular processes. Recently, several small protein domains have been identified that appear to function in these various protein-protein interactions. Two such domains are Src homology 2 (SH2) and Src homology 3 (SH3) (Musacchio, A. et al. (1994) Prog. Biophys. Mol. Biol. 61: 283-297).
SH3 domains, defined by their homology to a region of the proto-oncogene c-Src, are small protein domains of 50 to 60 amino acids found in a diverse group of proteins. SH3 domains bind to proline-rich ligands and are involved in a number of cellular processes including subcellular localization, G-protein signaling, and tyrosine kinase regulation. Proteins which contain SH3 domains are important for cellular organization and the control of cellular morphology. Several proteins associated with the cytoskeleton, including (.alpha.-spectrin and myosin-1, contain SH3 domains (Pawson, T. et al. (1992) Cell 71:359-362). The small GTP-binding protein Rho binds with high affinity to SH3 domains, is involved in actin bundling, and regulates the assembly of focal adhesions (Ridley, A. J. et al. (1992) Cell 70:389-399).
Formins are a small group of proline-rich phosphoproteins which are localized largely in the nucleus and are required for proper limb and kidney development in the mouse (Chan, D. C. et al. (1996) EMBO J. 15: 1045-54). Formins appear to function by interacting with certain SH3-containing proteins (formin binding proteins, FBP) that are expressed during mouse embryogenesis. In addition to three SH3-containing FBPs (FBP1, FBP17, and FBP27), five FBPs containing an "SH3-like" binding motif have also been identified. The new motif, termed WWP/WW because of highly conserved tryptophan and proline residues, compete with the SH3-containing FBPs for binding to proline-rich regions of formin. Chan et al. (supra) suggest that this competition may serve to regulate the function of SH3 domains in these interactions.
SH3 domains are characterized by a conserved structure composed of two antiparallel, B-pleated sheets packed against each other at rights angles. This packing forms a hydrophobic pocket lined with residues that are highly conserved between different SH3 domains. The hydrophobic pocket makes critical hydrophobic contacts with proline residues in the ligand binding protein (Feng, S. et al. (1994) Science 266: 1241-47). Electrostatic interactions are also sometimes important for specificity. In FBP17, for example, the sequence ALYTF is similar to the highly conserved ALYDY sequence in many SH3 domains. The Y or F in position five of this sequence is thought to be part of the hydrophobic binding pocket of SH3. W.sub.204 and Y.sub.221 in FBP17 are also thought to be important for ligand binding.
The regulation of protein interactions by SH3-containing proteins has implications in various diseases. Regulation of protein tyrosine kinase activity by SH3-containing proteins may be important in controlling some types of cancer. It is well known that cellular transformation (oncogenesis) is often accompanied by increased tyrosine kinase activity (Charbonneau, H. and N.K.Tonks (1992) Annu. Rev. Cell Biol. 8:463-93). SH3-containing proteins are important in the immune response and immune disorders. In phagocytes, the NADPH oxidase mutiprotein complex is activated by inflammatory stimuli to produce superoxide, a precursor for antimicrobial oxidants. This activation is dependent on the interaction of SH3-containing oxidase proteins p47-phox, p67-phox, and p40-phox with other proteins of the oxidase complex (McPhail, L. C. (1994) J. Exp. Med. 180:2011-2015). The SH3 domains of p47-phox and p67-phox may be responsible for assembly of the functional oxidase complex (Pawson, supra).
The discovery of new SH3-containing proteins and the polynucleotides encoding them satisfy a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of cancer, and immune and developmental disorders.